The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention includes a method for predicting the compressive strength of such a hardenable mixture, which is very important for planning a project. The invention further provides means to produce fly ash of a desired size modulus with a 100% yield in desirable production quantities for use in hardenable mixtures, along with hardenable mixtures comprising cement and fly ash which can achieve greater compressive strength than hardenable mixtures containing only cement without fly ash over the time period relevant for construction. Also provided is a method for the continuous production of fly ash with a 100% yield in desirable production quantities.
Fly ash, a by-product of coal burning power plant, is produced worldwide in large quantities each year. In 1988, approximately 84 million tons of coal ash were produced in the U.S. in the form of fly ash (60.7%), bottom ash (16.7%), boiler slag (5.9%), and flue gas desulfurization (16.7%) (Tyson, 1990, Coal Combustion By-Product Utilization Seminar, Pittsburgh, 15 pp.). Out of the approximately 50 million tons of fly ash generated annually, only about 10 percent is used in concrete (ACI Committee 226, 1987, xe2x80x9cUse of Fly Ash In Concrete,xe2x80x9d ACI 226.3R-87, ACI J. Proceedings 84:381-409) while the remaining portion is mostly disposed of as waste in landfills.
It is generally more beneficial for a utility to sell its ash, even at low or subsidized prices, rather than to dispose of it in a landfill, since this will avoid the disposal cost. In the 1960""s and 70""s the cost of ash disposal was typically less than $1.00 per ton. However, due to the more stringent environmental regulations starting in the late 1970""s, the cost of ash disposal has rapidly increased to from $2.00 to $5.00 per ton and is still rising higher (Bahor and Golden, 1984, Proceedings, 2nd International Conference on Ash Technology and Marketing, London, pp. 133-136). The shortage of landfill due to environmental concerns has further escalated the disposal cost. The Environmental Protection Agency (EPA) estimated in 1987 that the total cost of waste disposal at coal fired power plants ranged from $11.00 to $20.00 per ton for fly ash and bottom ash (Courst, 1991, Proceedings: 9th International Ash Use Symposium, 1:21-1 to 21-10). This increasing trend of disposal cost has caused many concerns and researchers are urgently seeking means for better utilization of fly ash. One potential outlet for fly ash is incorporation in concrete or mortar mixtures.
Fly ash is used in concrete in two distinct ways, one as a replacement for cement and the other as a filler. The first use takes advantage of the pozzolanic properties of fly ash, which, when it reacts with lime or calcium hydroxide, can enhance the strength of cementitious composites. However, fly ash is relatively inert and the increase in compressive strength can take up to 90 days to materialize. Also, since fly ash is just a by-product from the power industry, the quality of fly ash has always been a major concern to the end users in the concrete industry.
Incorporation of fly ash in concrete improves workability and thereby reduces the water requirement with respect to the conventional concrete. This is most beneficial where concrete is pumped into place. Among numerous other beneficial effects arc reduced bleeding, reduced segregation, reduced permeability, increased plasticity, lowered heat of hydration, and increased setting times (ACI Committee 226, 1987, supra). The slump is higher when fly ash is used (Ukita et al., 1989, SP-1 14, American Concrete Institute, Detroit, pp.219-240).
However, the use of fly ash in concrete has many drawbacks. For example, addition of fly ash to concrete results in a product with low air entrainment and low early strength development.
As noted above, a critical drawback of the use of fly ash in concrete is that initially the fly ash significantly reduces the compressive strength of the concrete. Tests conducted by Ravindrarajah and Tam (1989, Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SP-114, American Concrete Institute, Detroit, pp. 139-155) showed that the compressive strength of fly ash concrete at early ages are lower than those for the control concrete, which is a general property of concrete or mortar when fly ash is added. Most of the reported studies tend to show a lower concrete strength due to the presence of fly ash; none has yet suggested a solution to actually enhance the property of concrete economically. Yet, for fly ash to be used as a replacement for cement, it must be comparable to cement in terms of strength contribution at a point useful in construction. As a practical matter, this means that the fly ash concrete must reach an acceptable compressive strength within about 2 weeks.
Swamy (1984, Proceedings, 2nd International Conference on Ash Technology and Marketing, London, pp. 359-367) showed that 30% replacement by weight, and inclusion of a high dose of a superplasticizer, yielded concrete with material properties and structural behavior almost identical to those of concrete of similar strength without fly ash. However, due to the high cost of superplasticizer, mix proportions were not economical.
Fly ashes from different sources may have different effect to concrete. The same fly ash may behave differently with Portland cements of different types (Popovics, 1982, ACI J. Proceedings 79:43-49), since different types of Portland cement (type I to V) have different chemical composition. Other factors relating to the effects of fly ash on concrete that are not presently understood are lime availability, the rate of solubility and reactivity of the glassy phase in different fly ash, and the proper mix proportion to ensure early strength development of fly ash concrete.
Fly ash particles are typically spherical, ranging in diameter from 1 to 150 microns (Berry and Malhotra, 1980, ACI J. Proceedings 77:59-73). Aitcin et al. (1986, Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SP-91, American Concrete Institute, Detroit, pp. 91-113) showed that if the average diameters, D50, of fly ash are smaller, the surface area of the fly ash will be larger than those with larger average diameters. Many factors affect the size or average diameter of fly ash, including storage conditions, ash collection processes, and combustion conditions. Combustion conditions are perhaps most important, because these determine whether carbon remains in the ash or if combustion is complete.
There are two main forms of combustion: dry bottom boiler combustion and wet bottom boiler combustion. The main difference between the two types of boiler is that wet bottom boilers reach the fusion temperature of ash, thus resulting in fly ash with greater glass characteristics.
There are generally two methods known to measure the fineness of fly ash. The first is by measuring the residue on the 45 micron (No. 325 sieve), which is the method used in the United States. The second method is the surface area method by air permeability test. Lane and Best (1982, Concrete International: Design and Construction 4:81-92) suggested that 45 microns sieve residue is a consistent indicator of pozzolanic activity. For use in concrete or mortar, ASTM C 618 (1990, ASTIM C 618-89a, Annual Book of ASTM Standards, Vol. 04.02) specifies that not more than 34% by weight of a given fly ash be retained on a 45 microns sieve. However, Ravina (1980, Cement and Concrete Research 10:573-580) reported that specific surface area provides a more accurate indicator of pozzolanic activity.
Research carried out by Ukita et al. (1989, supra) purported that as the percentage of finer particles, i.e., those particles ranging from diameters of 1 to 20 microns, in concrete increases, the corresponding strength gain is notable. Similar observations have been reported by Giergiczny and Werynska (1989, Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SSP-114, American Concrete Institute, Detroit, pp. 97-115).
Both of the groups mentioned above describe results with fly ash of disparate characteristics and sources, but did not include controls for these variable. Thus, although the emphasis of these reports is on the performance of finer particle fly ashes, the variables introduced into the studies lead to reservations with respect to any conclusions that may be drawn. In particular, Ukita et al. (1989, supra) collected fly ash from different locations. However, an earlier report demonstrated that fly ashes collected from different locations have different chemical properties (Liskowitz et al., 1983, xe2x80x9cSorbate Characteristic of Fly Ash,xe2x80x9d Final Report, U.S. Dept. of Energy, Morgantown Energy Technology Center, p. 211). Giergiczny and Werynska (1989, supra) ground the original fly ash into different sizes. Grinding can add metal particles into the fly ash, and also tends to yield unnaturally shaped particles of fly ash. Thus, these reports fail to provide conclusive information about the effect of fine particle size on the properties imparted by fly ash.
Berry et al. (1989, Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, SP-114, American concrete Institute, Detroit, pp. 241-273) studied the properties of fly ash with particle size smaller than 45 microns, so called xe2x80x9cbeneficiatedxe2x80x9d fly ash, in mortar. Fly ashes of this particle size showed improved pozzolanic activity, reduced water demand and enhanced ability to reduce alkali-aggregate reactivity.
Although beneficiated fly ash seem to show promising results in terms of improved performance of mortar, other researchers concluded otherwise when used in concrete. Giaccio and Malhotra (1988, Cement, Concrete, and Aggregates 10:88-95) also conducted the test using the beneficiated fly ashes. They showed that the concrete made with ASTM type I cement, the use of beneficiated fly ash and condensed silica fume did little to enhance the properties of concrete compared with the raw fly ash.
As explained above, efforts have been made to grind fly ash recovered from boilers so that they have a particle size in order to increase their pozzolanic activity and thus substitute for pozzolanic materials such as cement having comparable contribution at a point useful in construction as concrete that does not use fly ash. Grinding the fly ash has met with only limited success. There are numerous means to grind fly ash so that it can be used as a pozzolanic material. One such method involves grinding the fly ash with a grinding medium, such as zirconium silicate particles. In particular, Perry""s Chemical Engineers Handbook, 6TH Edition, teaches that in order to grind fly ash into particles having an appropriate size for use as a substitute for cement in concrete or mortar, the volume of fly ground should be equal to or greater than the void volume of the grinding material [page 8-32 of Perry""s Handbook, 6th Edition]. However, these grinding methods have met with only limited success in that the yield of fly ash particles having a diameter less than about 12 xcexcm is low. As a result, much fly ash is wasted, and the grinding process is not economical.
Accordingly, what is needed are methods of grinding fly ash into particles that have a size that permits its use in concrete or mortar that undergo strength development comparable to, or superior to concrete and mortar comprising no fly ash, and which are readily used in the construction industry.
There is also a need utilize all of the fly ash produced in coal-dust fired boilers, thus decreasing the amount of waste produced by boilers, and decreasing the amount of cement used in the construction industry.
There is a further need to process fly ash efficiently to provide about 100% yield of useful product in desirable production quantities.
There is a further need in the art for high strength concrete and mortar containing fly ash.
There is yet a further need in the art for the utilization of fly ash generated during coal combustion.
These and other needs in the art are addressed in the instant application.
The citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.
The present invention relates to hardenable mixtures comprising processed fly ash of a defined fineness as a replacement for cement in cementitious materials, which hardenable mixtures achieve compressive strength that is about equal to or greater than the compressive strength of the same hardenable mixture without fly ash in a time period that is acceptable for construction and other applications. In particular embodiments, the hardenable mixture can be concrete or mortar, as hereinafter defined.
The invention is related to the invention disclosed and claimed in U.S. Pat. No. 5,624,491 and in International Patent Publication No. WO 95/32423, published Nov. 30, 1995, of PCT International Patent Application No. PCT/US95/06182, both entitled xe2x80x9cIMPROVED COMPRESSIVE STRENGTH OF CONCRETE AND MORTAR CONTAINING FLY ASH,xe2x80x9d each of which is incorporated herein by reference in their entireties. However, the present invention is based on the discovery that fly ash having desirable characteristics, such as a fineness modulus as defined in U.S. Pat. No. 5,624,491 and International Publication No. WO 95132423 (PCT/US95/06182), can be prepared by dry processing fly ash from boilers so as to shift the entire distribution of sizes to a desired range, while retaining substantially uniform spherical shape of the processed fly ash. This invention advantageously avoids the need for size fractionation, e.g., by air classification, and provides a product with approximately 100% yield in desirable production quantities that, when incorporated in a hardenable mixture, such as concrete or mortar, demonstrates compressive strength properties that are equal to or better than fractionated fly ash achieves with such classification methodology, such as air classification.
Broadly, the present invention extends to fly ash characterized by:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c. a median particle diameter of less than about 4.0 xcexcm; and
b. a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
Furthermore, the present invention extends to fly ash as described above, wherein greater than about 93% of the particles have a diameter of less than 11 xcexcm, greater than about 70% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 18% of the particles have a diameter of less than 1.375 xcexcm.
In a particular embodiment, the present invention extends to fly ash characterized by having a median particle diameter of less than about 3.0 xcexcm.
Furthermore, the present invention extends to fly ash as described above, wherein the range of particle diameters is from about 0.9 xcexcm to about 62 xcexcm.
Furthermore, any type of fly ash described herein has applications in the invention. In a particular embodiment, the fly ash is prepared by grinding unfractionated fly ash. Methods of grinding fly ash are set forth infra.
The present invention further extends to concrete and mortar which utilize fly ash. In particular, the present invention extends to a concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water. The cementitious materials of concrete and mortar of the invention comprise from about 10% to about 50% by weight the fly ash characterized by:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c. a median particle diameter of less than about 4.0 xcexcm; and
b. a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
The concrete or mortar of this embodiment also comprises about 50% to about 90% by weight cement.
In addition, the present invention extends to a concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash characterized by:
a. substantially uniform spherical shape;
b. greater than about 93% of the particles have a diameter less than 11 xcexcm, greater than about 70% of the particles have a diameter less than 5.5 xcexcm, and greater than about 18% of the particles have a diameter of less than 1.375 xcexcm;
c. the median particle diameter is less than about 3.0 xcexcm; and
d. the range of particle diameters is from about 0.9 xcexcm to about 62 xcexcm, and about 50% to about 90% by weight cement.
Optionally, concrete of the invention as described above can further comprise silica fume, glass fibers, or a combination thereof.
In another embodiment the present invention extends to a mortar comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight the fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 m, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c. a median particle diameter of less than about 4.0 xcexcm; and
d. a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
In another embodiment, the present invention extends to a mortar comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cenientitious materials comprise from about 10% to about 50% by weight the fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 93% of the particles have a diameter less than 11 xcexcm, greater than about 70% of the particles have a diameter less than 5.5 xcexcm, and greater than about 18% of the particles have a diameter of less than 1.375 xcexcm;
c. the median particle diameter is less than about 3.0 xcexcm; and
d. the range of particle diameters is from about 0.9 xcexcm to about 62 xcexcm, and about 50% to about 90% by weight cement.
Optionally, a mortar of the invention can further comprise silica fume, glass fibers, or a combination thereof.
The present invention also extends to methods for preparing fly ash, so as to shift the size distribution of fly ash particles, such that the finished fly ash has the following characteristics:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c. a median particle diameter of less than about 4.0 xcexcm; and
d. a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
The present invention encompasses numerous methods of producing fly ash having characteristics as described above. One such method involves a fluidized bed grinding process. In particular, the present invention extends to a method for preparing fly ash as described above, wherein the processing comprises grinding with a fluidized bed grinding process such that the volume of fly ash ground in the process is less than the void volume of the grinding medium. As a result, the collisions between the fly ash and grinding medium occur at a sufficient frequency to grind the fly ash and shift the size distribution of fly ash particles. In a particular embodiment, the ratio of fly ash to grinding medium comprises about one part unfractionated fly ash to about seven parts grinding media (by weight). In another embodiment, the ratio of fly ash to grinding medium comprises about one part fly ash to about 4 parts grinding medium, by volume. It has been discovered that fly ash serves as a lubricant during the grinding process. As a result, the high temperatures that would be expected in a situation where the volume of fly ash is less than the void volume of the grinding medium are not realized.
Furthermore, numerous grinding medium have applications in the fluidized bed grinding process of the invention. Examples of grinding medium having applications herein include, but certainly are not limited to, zirconium silicate, carbon steel, chromium steel, or stainless steel, to name only a few.
Furthermore, the present invention extends to concrete and mortar compositions. More specifically, in one embodiment, the present invention extends to a concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a) substantially uniform spherical shape;
b) greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than about 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c) a median particle diameter of less than about 4.0 xcexcm; and
d) a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
Furthermore, a concrete of the invention, as described above, can further comprise glass fibers, silica fume, or a combination thereof.
In addition, the present invention extends to concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 93% of the particles have a diameter less than 11 xcexcm, greater than about 70% of the particles have a diameter less than 5.5 xcexcm, and greater than about 18% of the particles have a diameter of less than 1.375 xcexcm;
c. the median particle diameter is less than about 3.0 xcexcm; and
d. the range of particle diameters is from about 0.9 xcexcm to about 62 xcexcm, and about 50% to about 90% by weight cement.
Naturally, a concrete of the invention as described above, can further comprise silica fume glass fibers, or a combination thereof.
Also, the present invention extends to a mortar comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a) substantially uniform spherical shape;
b) greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than about 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c) a median particle diameter of less than about 4.0 xcexcm; and
d) a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
In another embodiment, mortar of the invention comprises about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 93% of the particles have a diameter less than 11 xcexcm, greater than about 70% of the particles have a diameter less than 5.5 xcexcm, and greater than about 18% of the particles have a diameter of less than 1.375 xcexcm;
c. the median particle diameter is less than about 3.0 xcexcm; and
d. the range of particle diameters is from about 0.9 xcexcm to about 62 )m, and about 50% to about 90% by weight cement.
What""s more, a mortar of the invention, as described above, can further comprise glass fibers, silica fume, or a combination thereof.
Moreover, the present invention extends to a method for preparing fly ash comprising processing fly ash so as to shift the size distribution to have the following characteristics:
a) substantially uniform spherical shape;
b) greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than about 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c) a median particle diameter of less than about 4.0 xcexcm; and
d) a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm.
In particular, the present invention extends to a method of preparing fly ash as described above, wherein the processing comprises grinding fly ash with a fluidized bed grinding process using a ratio of one part unfractionated fly ash with seven parts grinding medium (by weight).
Numerous grinding media are readily available to the skilled artisan and have applications in a method of the invention. Particular examples include zirconium silicate, stainless steel, or carbon steel, to name only a few.
Furthermore, fly ash ground in a method of the invention can be dry bottom boiler or wet bottom boiler fly ash.
Furthermore, the present invention extends to fly ash prepared so as to shift the size distribution to have the following characteristics:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 12 xcexcm, greater than about 50% of the particles have a diameter of less than 5 xcexcm, and greater than about 15% of the particles have a diameter of less than 2.3 xcexcm;
c. a median particle diameter of less than about 6.0 xcexcm; and
d. a range of particle diameters of from about 0.78 xcexcm to about 30 xcexcm.
In a particular embodiment, fly ash prepared to shift the size distribution as described above is by grinding the fly ash with a grinding medium in a non-expanded bed, wherein the volume of fly ash is less than the void volume of the grinding medium. For example, in one embodiment of the invention, the ratio of fly ash to grinding medium in the non-expanded bed grinding process is about 1 part fly ash to about 4 parts grinding medium, by volume. In another embodiment, the ratio of fly ash to grinding medium comprises about 1 part fly ash to about 18 parts grinding medium, by weight. Naturally, numerous grinding medium are available to with the requisite specific gravity for using in producing fly ash as described above. Examples include, but certainly are not limited to carbon steel or stainless steel. In a particular embodiment of the invention, the grinding medium comprises carbon steel spheres having a diameter of about xe2x85x9 inch. 
In yet another embodiment, the present invention extends to a concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a) substantially uniform spherical shape;
b) greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than about 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 1.375 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c) a median particle diameter of less than about 4.0 xcexcm; and
d) a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm,
wherein the fly ash is prepared by grinding fly ash with a grinding medium with a fluidized bed grinding process such that the volume of fly ash ground in the process is less than the void volume of the grinding medium. In a particular embodiment, the ratio of fly ash to grinding medium comprises about one part unfractionated fly ash to about seven parts grinding media (by weight).
In addition, the present invention extends to a concrete as described above, wherein the grinding medium comprises zirconium silicate, stainless steel or carbon steel. In addition, optionally, the concrete can further comprises glass fibers, silica fume, or a combination thereof. In a preferred embodiment, the grinding medium comprises zirconium silicate with a diameter of about 2-2.5 mm.
Moreover, the present invention extends to a mortar comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a) substantially uniform spherical shape;
b) greater than about 90% of the particles have a diameter of less than 11 xcexcm, greater than about 60% of the particles have a diameter of less than about 5.5 xcexcm, greater than about 60% of the particles have a diameter of less than 5.5 xcexcm, and greater than about 15% of the particles have a diameter of less than 1.375 xcexcm;
c) a median particle diameter of less than about 4.0 xcexcm; and
d) a range of particle diameters of from about 0.1 xcexcm to about 70 xcexcm,
wherein the fly ash is prepared by grinding fly ash with a grinding medium with a fluidized bed grinding process such that the volume of fly ash ground in the process is less than the void volume of the grinding medium. In a particular embodiment, the ratio of fly ash to grinding medium comprises about one part unfractionated fly ash to about seven parts grinding media (by weight). Furthermore, just as with concrete of the invention, numerous grinding media can be used in a mortar of the invention. Examples of grinding medium having applications herein include, but are not limited to zirconium silicate, carbon steel, or stainless steel. In a particular embodiment, the grinding medium comprises zirconium silicate having a diameter of about 2-2.5 mm.
Furthermore, the present invention extends to a mortar as described above, further comprising glass fibers, silica fume, or a combination thereof.
In another embodiment, the present invention extends to a concrete comprising fly ash prepared using a non-expanded grinding bed process. In particular, the present invention extends to a concrete comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, about 1 to about 5 parts by weight coarse aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 12 xcexcm, greater than about 50% of the particles have a diameter of less than 5 xcexcm. and greater than about 15% of the particles have a diameter of less than 2.3 xcexcm;
c. a median particle diameter of less than about 6.0 xcexcm; and
d. a range of particle diameters of from about 0.78 xcexcm to about 30 xcexcm.
The fly ash of this concrete of the invention is prepared by grinding the fly ash with a grinding medium in a non-expanded bed, wherein the volume of fly ash in the non-expanded bed is less than the void volume of the grinding medium. Numerous grinding medium have applications in a non-expanded bed grinding process involved in the concrete of the invention. In an embodiment, the ratio of fly ash to grinding medium comprises about 1 part fly ash to about 4 parts grinding medium by volume. In another embodiment, the ratio of fly ash to grinding medium comprises about 1 part fly ash to about 18 parts grinding medium by weight. Particular examples of grinding medium include, but are not limited to carbon steel or stainless steel. In a particular embodiment of concrete, the grinding medium comprises carbon steel having a diameter of about xe2x85x9 inch.
Moreover, the present invention extends to a concrete as described above, further comprises glass fibers, silica fume, or a combination thereof.
Naturally, the present invention extends to a mortar comprising fly ash prepared using a non-expanded grinding bed process. More specifically, the present invention extends to a mortar comprising about 1 part by weight cementitious materials, about 1 to about 3 parts by weight fine aggregate, and about 0.35 to about 0.6 parts by weight water, wherein the cementitious materials comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement. The cementitious materials of mortar of the invention comprise from about 10% to about 50% by weight fly ash and about 50% to about 90% by weight cement, wherein the fly ash is characterized by:
a. substantially uniform spherical shape;
b. greater than about 90% of the particles have a diameter of less than 12 xcexcm, greater than about 50% of the particles have a diameter of less than 5 xcexcm, and greater than about 15% of the particles have a diameter of less than 2.3 xcexcm;
c. a median particle diameter of less than about 6 xcexcm; and
d. a range of particle diameters of from about 0.78 xcexcm to about 30 xcexcm.
The fly ash of mortar of the invention is prepared by grinding the fly ash with a grinding medium in a non-expanded bed, wherein the volume of fly ash in the non-expanded bed is less than the void volume of the grinding medium. In an embodiment of the invention, the ratio of fly ash to grinding medium in the non-expanded bed comprises about 1 part fly ash to about 4 parts grinding medium by volume. In another embodiment, the ratio of fly ash to grinding medium comprises about 1 part fly ash to about 18 parts grinding medium, by weight.
Numerous grinding media have applications in a mortar of the invention as described above. Examples include, but certainly are not limited to carbon steel or stainless steel. In a particular embodiment, the grinding medium comprises carbon steel, having a diameter of about xe2x85x9 inch.
Moreover, numerous types of fly ash have applications in methods, concrete, or mortar of the invention. Particular examples include dry bottom fly ash, or wet bottom fly ash.
An important advantage of the present invention relates to the improved compressive strength properties contributed by the processed fly ash hardenable mixtures. For example, in mortar prepared using processed fly ash of the invention to replace 25% of the cement, xe2x80x9ccross-overxe2x80x9d in compressive strength of the mortar compared with a control mortar occurs within 7 to 14 days, and the compressive strength of the mortar containing processed fly ash is 50% greater than the control after 56 days.
As noted above, another advantage of the invention is that the process does not require fractionation, and allows for utilization of about 100% of the fly ash obtained from a boiler operation to produce desirable production quantities of fly ash. Quantitative utilization of the fly ash avoids the need to dispose of undesirable fly ash fractions, which addressed the concerns of utilities for abatement of this otherwise undesirable pollutant.
A further advantage of the invention is that the grinding process appears to release ammonia captured in the surface of fly ash produced from urea-treated coal (which is used to reduce NOx emissions). The presence of ammonia in fly ash renders it unsuitable for use in concrete or mortar.
Yet another advantage of the present invention is that processing minimizes the effects of boiler conditions on the fly ash properties associated with boiler conditions and the degree of coal pulverization, such that the fly ash is desirable as a cement replacement in hardenable mixtures. Accordingly, fly ash can be dry bottom boiler fly ash or wet bottom boiler fly ash.
As is readily apparent to one of ordinary skill in the art, selection of starting material and grinding conditions are necessary to yield the fly ash of the invention. In a specific embodiment exemplified herein, unfractionated (unclassified) fly ash unexpectedly yields a superior processed fly ash product after grinding; a coarse fraction of fly ash does not yield the same quality processed fly ash product under the same grinding conditions.
Furthermore, one of ordinary skill in the art can readily use a method of the invention set forth below, particularly a method of grinding fly ash in a non-expanded bed, to produce fly ash readily usable in various industries, in desired production quantities, i.e, approximately three tons per hour.
In a further aspect, in a hardenable mixture, i.e., concrete or mortar, of the invention, the fine aggregate may comprise sand and fly ash, wherein a ratio by weight of sand to fly ash is from about 4:1 to about 1:1. Preferably, the fly ash has a fineness modulus of less than about 600, wherein the fineness modulus is calculated as the sum of the percent of fly ash retained on sieves of 0, 1, 1.5, 2, 3, 5, 10, 20, 45, 75, 150, and 300 microns (as described in U.S. Pat. No. 5,624,491 and International Publication No. WO 95/32423). In another embodiment, the fly ash used as fine aggregate is processed fly ash of the invention.